1. Field of the Invention
The present invention relates to a discharge device used as a sterilizer module for air purification, and, more particularly, to a surface discharge type air cleaning device that is capable of increasing generation of hydroxyl (OH) radicals while decreasing generation of ozone, which is toxic to humans, thereby increasing discharge safety and improving noxious gas sterilizing efficiency and air cleaning efficiency.
2. Description of the Related Art
Generally, a surface discharge type air cleaning device adopts a surface discharge plasma chemical processing method. Specifically, the surface discharge type air cleaning device is a ceramic-based high frequency discharge type air cleaning device that is capable of generating a large number of hydroxyl radicals and a large amount of ozone through the formation of a strong plasma area on the surface of an element and processing noxious gases through the use of the generated hydroxyl radicals and ozone.
FIG. 1 is a plan view showing a conventional surface discharge type air cleaning device, and FIG. 2 is a cross-sectional view of the conventional surface discharge type air cleaning device seen from line A-A of FIG. 1.
As shown in FIGS. 1 and 2, the conventional surface discharge type air cleaning device comprises: an insulating dielectric body 10, which is composed of two rectangular sheets attached to each other while being disposed in surface contact with each other; a discharge electrode 12 disposed on the upper surface of the insulating dielectric body 10; and a ground electrode 14 disposed between the two rectangular sheets of the insulating dielectric body 10. On the upper surface of the insulating dielectric body 10 is applied a coating layer 16 for covering the discharge electrode 12 such that the discharge electrode 12 is not directly exposed to the atmosphere.
Generally, the insulating dielectric body 10 is made of a ceramic material. The discharge electrode 12 is connected to one terminal of a power source supply unit, and the ground electrode 14 is connected to the other terminal of the power source supply unit, such that the power source is supplied to not only the discharge electrode 12 but also the ground electrode 14. An alternating current power source is used as the power source.
The discharge electrode 12 comprises: three main electrodes 12a, which are arranged in parallel with one another; and subsidiary electrodes 12b protruding from the main electrodes 12a, each of the subsidiary electrodes 12b having a pointed end. The ground electrode 14 comprises: two branched ground electrodes 14a, which are arranged in parallel with each other and disposed opposite to the subsidiary electrodes 12b. 
When a power source having a voltage higher than onset voltage is applied to the discharge electrode 12 and the ground electrode 14 of the conventional surface discharge type air cleaning device with the above-stated construction, a dielectric breakdown phenomenon occurs between the discharge electrode 12 and the ground electrode 14. As a result, a discharge phenomenon occurs on the surface of the insulating dielectric body 10, as shown in FIG. 3, and therefore, a strong plasma area is formed on the surface of the insulating dielectric body 10.
When the plasma is discharged as described above, a conductive path, which is called a streamer, is formed on the surface of the insulating dielectric body 10, and a large number of high-energy electrons are generated through the streamer. The high-energy electrons react with gases surrounding the high-energy electrons due to electron collision. As a result, a large amount of ozone and a large number of hydroxyl radicals and negative ions are generated.
The generated ozone, hydroxyl radicals, and negative ions oxidize and decompose pollutants, such as noxious gases contained in air, to clean the air.
As described above, the conventional surface discharge type air cleaning device performs discharge through the entire surface of the insulating dielectric body 10, and therefore, the onset voltage of the conventional surface discharge type air cleaning device is lower than that of a corona discharge type air cleaning device. Consequently, power consumption is low, and noise generated from the conventional surface discharge type air cleaning device is small, and therefore, air is efficiently cleaned by the conventional surface discharge type air cleaning device even when the conventional surface discharge type air cleaning device is used in a small space.
In the conventional surface discharge type air cleaning device, however, the discharge electrode 12 is disposed on the upper surface of the insulating dielectric body 10, i.e., the pattern of the discharge electrode 12 is formed on the upper surface of the insulating dielectric body 10 in an embossed structure. As a result, there is a limit in lowering the onset voltage and input energy necessary to cause discharge. Consequently, the number of hydroxyl radicals and negative ions, which are generated when the voltage is low, is decreased, and the amount of ozone, which is toxic to humans, is increased. In addition, power consumption is increased.
Specifically, electrical charge concentration is increased at the end part E of the discharge electrode 12, as shown in FIG. 3. Consequently, it is required that the onset voltage and the input energy be raised in order to accomplish uniform generation distribution of streamer throughout the entire region of the dielectric body. Especially, thermal stress is partially increased at the end part E of the discharge electrode 12, and therefore, gases surrounding the discharge electrode 12 are heated. As a result, the amount of ozone generated is increased. On the other hand, the number of hydroxyl radicals and negative ions is decreased. Also, partial deterioration of the electrode occurs rapidly due to partial increase of thermal stress, and therefore, the service life of the surface discharge type air cleaning device is shortened, and discharge safety is also lowered. Consequently, air cleaning efficiency is decreased.
Furthermore, the insulating dielectric body 10 of the conventional surface discharge type air cleaning device is composed of two sheets, between which the ground electrode 14 is disposed. Consequently, the structure of the conventional surface discharge type air cleaning device is complicated, and therefore, manufacturing costs of the conventional surface discharge type air cleaning device are increased.